President Barack Obama is stepping up military aid to Syria’s rebels after concluding that the regime of Syrian President Bashar Al-Assad used chemical weapons against rebels there, the White House said Thursday.

Deputy National Security Adviser Ben Rhodes said in a statement that U.S. intelligence agencies had concluded that between 100 and 150 Syrians have died from the chemical weapons use.

The president “has said that the use of chemical weapons would change his calculus and it has,” Rhodes told reporters on a conference call. “Following on the credible evidence that the regime has used chemical weapons against the Syrian people, the President has augmented the provision of non-lethal assistance to the civilian opposition, and also authorized the expansion of our assistance to the Supreme Military Council.”

Obama had previously declared that chemical weapons use would cross a “red line” that would lead to greater U.S. involvement. Aides said Thursday some of the stepped-up aid would be a direct result of the regime’s decision to use chemical weapons.

“The Assad regime should know that its actions have led us to increase the scope and scale of the assistance that we provide to the opposition, including direct support to the SMC — the military option on the ground. We will continue to increase these efforts will increase going forward,” said Rhodes.

Just before the White House announcement, Sen. John McCain (R-Ariz.), one of the strongest advocates of greater U.S. support for the rebels, said Obama had decided to send arms to the opposition.

“The President of the United States will be announcing that it is now conclusive that Bashar Assad and the Syrian butchers have used chemical weapons,” McCain said on the Senate floor. “The president also will announce that we will be assisting the Syrian rebels in Syria by providing them with weapons and other assistance. I applaud the president’s decision.”

Despite McCain’s declaration that U.S. weapons are headed to the rebels, the White House would not go that far publicly. Indeed, Rhodes was cagey about what type of equipment would be provided.

“I can’t go through an inventory of the type of assistance we are going to provide,” Rhodes told reporters on a conference call. “It’s going to be substantively different from what we were providing certainly before our initial [chemical weapons] assessment in April….It’s going to be an increase on both the political and the military side.”

Rhodes said the U.S. help would have “direct military purposes for the SMC on the ground,” but he did not say whether it would take the form of offensive weaponry also known as “lethal aid,” defensive weapons or more modest equipment designed to fend off Assad’s forces.

“We are going to make decisions about further action on our own timeline,” Rhodes said, promising intensive consultations with Congress and U.S. allies.

The White House did say that Obama has not given his approval for a no-fly zone that would limit the Syrian regime’s ability to carry out attacks from the air on opposition forces and civilians.

“We have not made any decisions to pursued a military operation such as a n0-fly zone,” Rhodes said. “We have a range of contingency plans that were drawn up.”

House Intelligence Committee Chairman Mike Rogers (R-Mich.) said Monday he was “pleased” with Obama’s acknowledgement of chemical weapons use by the Syrians. However, Rogers pressed the president to move forward with the no-fly zone.

”The United States should assist the Turks and our Arab League partners to create safe zones in Syria from which the U.S. and our allies can train, arm, and equip vetted opposition forces,” Rogers said.

For more than a year, Obama has resisted pressure from both inside and outside the administration to provide military aid to the rebels. A variety of senior administration figures had advocated for U.S. provision of weapons to the opposition, including Secretary of State John Kerry and U.S. Ambassador to the United Nations Susan Rice, an administration official said Thursday.

Earlier this week, Kerry canceled a previously-planned trip to the Middle East in order to remain in Washington and participate in high-level discussions about the situation on Syria.

Then-Defense Secretary Leon Panetta and Joint Chiefs Chairman Gen. Martin Dempsey said at a Senate hearing in February that they favored such aid. Secretary of State Hillary Clinton was also reported to have backed greater assistance.

In the more skeptical camp were outgoing National Security Advisor Tom Donilon and Defense Secretary Chuck Hagel, the source said.

However, it has become apparent in recent months that the greatest opposition to military aid in Syria has come from Obama himself. Aides have been reluctant to outline his concerns, beyond saying he wanted to make sure that the intelligence regarding chemical weapons was as clear-cut as possible.

Former aides said Obama has a series of fears, including the prospect of the United States being drawn deeper and deeper into another war in the Arab world. The president was also gravely concerned that weapons could fall into the hands of Islamic militants who make up a substantial part of the armed opposition to Assad. In addition, Russia’s suggestions that it would provide additional advanced weapons to Assad fueled worries about a proxy war.

In its comments Thursday, the White House seemed to take care not to overstate the significance of the chemical weapons use in a conflict where conventional fighting has caused massive bloodshed.

“This is clearly a small portion of the catastrophic loss of life in Syria that now totals more than 90,000 deaths,” Rhodes said. However, he added, used of chemical weapons “crossed red lines that have existed in the international community for decades.”